ground limestone than the ordinary forms of air-slaked lime just 

 discussed. This so-called "sugar house" refuse lime will, in the dry 

 state, contain from 70 to 80 per cent of calcium carbonate and is 

 usually in a very fine state of division and for that reason is superior 

 to ground limestone, even ^though the latter may contain a larger 

 proportion of actual calcium carbonate. 



Even in the agricultural sense, the term lime does not include 

 gypsum. The latter is an entirely different substance from the three 

 named above, as will be explained later. Speaking with the correct- 

 ness of the chemist, the term "lime" is applied only to burnt lime 

 (quicklime) or calcium oxide. Just how the three materials dis- 

 cussed agriculturally under the name lime are to be employed and 

 where one is to be preferred to the other, if at all, are questions which 

 are answered below. 



Before going into a detailed discussion of the mission or function 

 of lime in soils, it is well to state clearly the relative values for practice 

 of (1) the burnt, caustic or quicklime; (2) the hydrated or water- 

 slaked lime, and (3) the carbonate or the air-slaked lime. These lime 

 materials are largely valued for the amount of calcium oxide which 

 they contain. Quicklime is nearly all calcium oxide. Hydrated or 

 water-slaked lime contains less calcium oxide than quicklime, in about 

 the following proportion: it takes 2643 pounds of hydrated lime to 

 carry an equivalent quantity of calcium oxide to that carried by one 

 ton of quicklime when both materials are pure. Nevertheless, for 

 practical purposes, they are not to be considered as very greatly differ- 

 ent, since the water-slaked lime contains certain advantages like that 

 of fineness of division, which the quicklime does not have, and since 

 they are rarely pure. Thoroughly air-slaked lime, like the sugar- 

 house refuse lime and ground limestone, contains only a little more 

 than half the amount of calcium oxide that the quicklime does and 

 therefore two tons of either should be employed if it is to be used in 

 place of the burnt lime. If the ground limestone is not very pure, 

 that is if it contains less than 98 per cent of calcium carbonate, pro- 

 portionately more, dependent upon the composition, as compared to 

 the burnt lime should be used. The same applies to the sugar-house 

 refuse lime. Just as the water-slaked lime has an advantage over the 

 burnt lime, owing to the fineness of division of the former, so the 

 sugar-house refuse lime possesses an advantage over the ground lime- 

 stone for the same reason. It must be remembered, however, in all 



